Sleep Cycle

Sleep normally follows a typical pattern that can be measured using EEG. A typical sleep has 4-5 cycles, each lasting 90-110 minutes.

1. Non-REM (NREM) Sleep:

N1(light sleep):

➛As wakefulness declines, alpha-activity (8-13Hz) disappeares & slow theta (4-7Hz) and delta (0.5-2Hz) activity emerges.
➛It lasts only a few minutes but may recur following body movements.
➛Sudden twitches & hypnic jerks are seen.
➛Hypnogogic hallucinations may also be seen
➛During N1, there is loss of some muscle tone & conscious awareness of the external environment.

N2:

➺It is characterized by
⭒Sleep spindles (0.5s phases fast activity ranging from 11-16Hz)
(max at vertex)
⭒K-complexes (symmetrical high-voltage vertex waves)
➺Arise spontaneously & in response to sudden stimuli
➺Muscular activity decreased conscious awareness of the external environment disappears.
➺N2 occupies 45-55% of total sleep in adults.
➺Lasts 15-30mts.

N3 (Deep or slow wave sleep [SWS]):

➻It is characterized by minimum of 20% delta waves (0.5-2Hz, Amplitude > 75 microV).
➻Night terrors, Nocturnal Enuresis & sleep walking are seen.
➻Lasts 30-40mts.

REM(Rapid Eye Movements) sleep:

➛Low voltage, desynehronized activity.
➛Muscle Antonia (paralysis may be necessary to protect organisms from self damage through physically acting out from vivid dreams that occur during this stage)
➛Myoclonia may be seen.
➛REM Sleep occupies 20-25% of total sleep in all ages.

Reference:

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